package main

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"os"
)

func check(e error) {
	if e != nil {
		panic(e)
	}
}
func main() {
	//Perhaps the most basic file reading task is slurping a file’s entire contents into memory.

	dat, err := ioutil.ReadFile("/tmp/dat")
	check(err)
	fmt.Print(string(dat))
	//You’ll often want more control over how and what parts of a file are read. For these tasks, start by Opening a file to obtain an os.File value.

	f, err := os.Open("/tmp/dat")
	check(err)
	//Read some bytes from the beginning of the file. Allow up to 5 to be read but also note how many actually were read.

	b1 := make([]byte, 5)
	n1, err := f.Read(b1)
	check(err)
	fmt.Printf("%d bytes: %s\n", n1, string(b1))
	//You can also Seek to a known location in the file and Read from there.

	o2, err := f.Seek(6, 0)
	check(err)
	b2 := make([]byte, 2)
	n2, err := f.Read(b2)
	check(err)
	fmt.Printf("%d bytes @ %d: %s\n", n2, o2, string(b2))
	//The io package provides some functions that may be helpful for file reading.
	// For example, reads like the ones above can be more robustly implemented with ReadAtLeast.

	o3, err := f.Seek(6, 0)
	check(err)
	b3 := make([]byte, 2)
	n3, err := io.ReadAtLeast(f, b3, 2)
	check(err)
	fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))
	//There is no built-in rewind, but Seek(0, 0) accomplishes this.

	_, err = f.Seek(0, 0)
	check(err)
	//The bufio package implements a buffered reader that may be useful both for its efficiency with many small reads and
	// because of the additional reading methods it provides.

	r4 := bufio.NewReader(f)
	b4, err := r4.Peek(5)
	check(err)
	fmt.Printf("5 bytes: %s\n", string(b4))
	//Close the file when you’re done (usually this would be scheduled immediately after Opening with defer).

	f.Close()
}
